In recent years, there has been a strong demand for crystalline, heat-resistant thermoplastic resins having a melting point of about 300.degree. C. or higher and permitting easy melt processing in the fields of the electronic and electric industry, automobile, aircraft and space industries.
Attention has recently given to poly(arylene thioether ketones) (hereinafter abbreviated as "PTKs") owing to their high melting points and PTKs have hence been studied.
There are disclosure on PTKs, for example, in Japanese Patent Laid-Open No. 58435/1985 (hereinafter referred to as "Publication A"), German Offenlegungsschrift 34 05 523Al (hererinafter referred to as "Publication B"), Japanese Patent Laid-Open No. 104126/1985, Japanese Patent Laid-Open No. 13347/1972, Indian J. Chem., 21A, 501-502 (May, 1982), Japanese Patent Laid-Open No. 221229/1986, U.S. Pat. No. 4,716,212 (hereinafter referred to as "Publication C"), U.S. Pat. No. 4,690,972, European Patent Publication No. 0,270,955 A2 (hereinafter referred to as "Publication D"), European Patent Publication No. 0,274,754 A2 (hereinafter referred to as "Publication E"), European Patent Publication No. 0,280,325 A2 (hereinafter referred to as "Publication F"), and European Patent Publication No. 0,285,874 A1 (hereinafter referred to as "Publication G").
Regarding the PTKs described in the above publications, neither molding nor forming has however succeeded to date in accordance with conventional melt processing techniques. Incidentally, the term "conventional melt processing techniques" as used herein means usual melt processing techniques for thermoplastic resins, such as extrusion, injection molding and melt spinning.
The unsuccessful molding or forming of PTKs by conventional melt processing techniques is believed to be attributed to &he very poor melt stability of the prior art PTKs, which tended to loss their crystallinity or to undergo crosslinking and/or carbonization, resulting in a rapid increase in melt viscosity, upon their melt processing.
It was attempted to produce some molded or formed products in Publications A and B. Since the PTKs had poor melt stability, certain specified types of molded or formed products were only obtained by a special molding or forming process, where PTKs were used only as a sort of binder, being impregnated into or mixed with a great deal of reinforcing fibers of main structural materials and molded or formed under pressure.
The present inventors conducted an extensive investigation with a view toward developing a process for economically producing a PTK which has melt stability permitting the application of conventional melt processing techniques. As a result, it was found that PTKs, which were improved significantly in melt stability compared to the conventional PTKs and hence permitted the application of conventional melt processing techniques (hereinafter referred to as "melt-stable PTKs"), can be obtained (Japanese patent Laid-Open No. 54031/1989).
Even such melt-stable PTKs were however still unable to avoid certain degrees of thermal modification and deterioration when melt-processed from powdery polymers into pellets or molded or formed products, whereby they underwent melt viscosity increase and/or decrease of crystallinity and develop sticking of thermal decomposition products to resin residence areas of melt processing equipment. They hence involved a problem that difficulties were encountered in determining appropriate conditions for their melt processing.
It therefore arose, as a subject to be investigated, to make further improvements to the melt stability of the melt-stable PTKs upon their melt processing.
The present inventors proceeded with an investigation in order to solve such a subject. As a result, it was found that when basic compounds such as the hydroxides and oxides of Group IA or IIA metals of the periodic table are added to the melt-stable PTK, their melt stability upon melt processing can be improved further (Japanese Patent Application No. 142772/1988).
It was however found that there are problems that when large amounts of such basic compounds are added to the melt-stable PTKs, their physical properties may possibly be lowered and the amounts to be added are hence limited involuntarily.